Immobilization of Enzymes on the Nano‐Au Film Modified Glassy Carbon Electrode for the Determination of Hydrogen Peroxide and Glucose

A new enzyme‐based amperometric biosensor for hydrogen peroxide was developed relying on the efficient immobilization of horseradish peroxidase (HRP) to a nano‐scaled particulate gold (nano‐Au) film modified glassy carbon electrode (GC). The nano‐Au film was obtained by a chitosan film which was first formed on the surface of GC. The high affinity of chitosan for nano‐Au associated with its amino groups resulted in the formation of nano‐Au film on the surface of GC. The film formed served as an intermediator to retain high efficient and stable immobilization of the enzyme. H₂O₂ was detected using hydroquinone as an electron mediator to transfer electrons between the electrode and HRP. The HRP immobilized on nano‐Au film maintained excellent electrocatalytical activity to the reduction of H₂O₂. The experimental parameters such as the operating potential of the working electrode, mediator concentration and pH of background electrolyte were optimized for best analytical performance of amperometry. The linear range of detection for H₂O₂ is from 6.1×10^?6 to 1.8×10^?3 mol L^?1 with a detection limit of 6.1 μmol L^?1 based on signal/noise=3. The proposed HRP enzyme sensor has the features of high sensitivity (0.25 Almol^?1cm^?2), fast response time (t_90%≤10 s) and a long‐term stability (>1 month). As an extension, glucose oxidase (GOD) was chemically bound to HRP‐modified electrode. A GOD/HRP bienzyme‐modified electrode formed in this way can be applied to the determination of glucose with satisfactory performance.     

Direct Electrochemistry of Glucose Oxidase Immobilized on Titanium Carbide‐Au Nanoparticles‐Fullerene C60 Composite Film and Its Biosensing for Glucose

The direct electrochemistry of glucose oxidase (GOD) immobilized on the designed titanium carbide‐Au nanoparticles‐fullerene C₆₀ composite film modified glassy carbon electrode (TiC‐AuNPs‐C₆₀/GCE) and its biosensing for glucose were investigated. UV‐visible and Fourier‐transform infrared spectra of the resulting GOD/TiC‐AuNPs‐C₆₀ composite film suggested that the immobilized GOD retained its original structure. The direct electron transfer behaviors of immobilized GOD at the GOD/TiC‐AuNPs‐C₆₀/GCE were investigated by cyclic voltammetry in which a pair of well‐defined, quasi‐reversible redox peaks with the formal potential (E^0′) of ‐0.484 V (vs. SCE) in phosphate buffer solution (0.05 M, pH 7.0) at the scan rate of 100 mV·s^?1 were obtained. The proposed GOD modified electrode exhibited an excellent electrocatalytic activity to the reduction of glucose, and the currents of glucose reduction peak were linearly related to glucose concentration in a wider linearity range from 5.0 × 10^?6 to 1.6 × 10^?4 M with a correlation coefficient of 0.9965 and a detection limit of 2.0 × 10^?6 M (S/N = 3). The sensitivity and the apparent Michaelis‐Menten constant (K_M^app) were determined to be 149.3 μA·mM^?1·cm^?2 and 6.2 × 10^?5 M, respectively. Thus, the protocol will have potential application in studying the electron transfer of enzyme and the design of novel electrochemical biosensors.     

Molecularly Imprinted Electrochemical Luminescence Sensor Based on Enzymatic Amplification for Ultratrace Isoproturon Determination

A new molecularly imprinted electrochemical luminescence sensor (MIP‐ECL sensor) was developed for isoproturon (IPU) determination based on the competition reaction between IPU and glucose oxidase labeled IPU (GOD‐IPU). After competition, hydrogen peroxide produced by residual GOD‐IPU on the MIP reacted with luminol to emit electrochemiluminescence (ECL) signal. The ECL intensity decreased when the GOD‐IPU molecules were replaced by IPU molecules in the samples. IPU could be determined in the concentration range from 9×10^?11 mol/L to 5.1×10^?9 mol/L with a detection limit of 3.78×10^?12 mol/L. Water samples were assayed and recoveries ranging from 98.5 % to 102.1 % were obtained.     

Fabrication of Bismuth/Multi-walled Carbon Nanotube Composite Modified Glassy Carbon Electrode for Determination of Cobalt

A bismuth/multi‐walled carbon nanotube (Bi/MWNT) composite modified electrode for determination of cobalt by differential pulse adsorptive cathodic stripping voltammetry is described. The electrode is fabricated by potentiostatic pre‐plating bismuth film on an MWNT modified glassy carbon (GC) electrode. The Bi/MWNT composite modified electrode exhibits enhanced sensitivity for cobalt detection as compared with the bare GC, MWNT modified and bismuth film electrodes. Numerous key experimental parameters have been examined for optimum analytical performance of the proposed electrode. With an adsorptive accumulation of the Co(II)‐dimethylglyoxime complex at ?0.8 V for 200 s, the reduction peak current is proportional to the concentration of cobalt in the range of 4.0×10^?10?1.0×10^?7 mol/L with a lower detection limit of 8.1×10^?11 mol/L. The proposed method has been applied successfully to cobalt determination in seawater and lake water samples.     

Label-Free Detection of DNA Hybridization Based on MnO2 Nanoparticles

Abstract

Nano-MnO₂/chitosan composite film modified glassy carbon electrode (MnO₂/CHIT/GCE) was fabricated and a DNA probe was immobilized on the electrode surface. The immobilization and hybridization events of DNA were characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The EIS was applied to the label-free detection of the target DNA. The human immunodeficiency virus (HIV) gene fragment was successfully detected by this DNA electrochemical sensor. The dynamic detection range was from 2.0 × 10^?11 to 2.0 × 10^?6 mol/L, with a detection limit of 1.0 × 10^?12 mol/L.     

Preparation of Polypyrrole/Nuclear Fast Red Films on Gold Electrode and Its Application on the Electrocatalytic Determination of Methyl‐dopa and Ascorbic Acid

A novel voltammetric method using the Ppyox/NFR/Au (poly pyrrole – nuclear fast red – gold) modified electrode was developed for simultaneous measurement of various combinations of ascorbic acid (AA) and methyldopa (MDA). Polypyrrole film was prepared by incorporation of nuclear fast red (NFR) as doping anion, during the electropolymerization of pyrrole onto a gold (Au) electrode in aqueous solution using cyclic voltammetric (CV) method, and then it was overoxidized at constant potential. Differential pulse voltammetry was utilized for the measurement of both analytes using modified electrode. Well‐separated voltammetric peaks were observed for ascorbic acid (AA) and methyldopa at the Ppyox/NFR/Au modified electrodes with peak separation of 0.210 V. It has been found that under optimum condition (pH 3.0), the oxidation of AA and MDA at the surface of the electrode occurs at a potential about 260 and 50 mV less positive than unmodified Au electrode respectively. The current catalytic oxidation peaks showed a linear dependent on the concentration of AA and MDA in the range of 9.0×10^?6 to 1.0×10^?3 and 1.0×10^?7 to 2.0×10^?5 mol L^?1 respectively. The detection limit of 5.8×10^?6 and 5.0×10^?8 mol L^?1 (S/N=3) were obtained for AA and MDA respectively. The modified electrode was used for determination of AA and MDA in some real samples such as human serum and tablet.     

Development and application of the tartrazine voltammetric sensors based on molecularly imprinted polymers

A modified glassy carbon electrode was prepared as an electrochemical voltammetric sensor based on molecularly imprinted polymer film for tartrazine (TT) detection. The sensitive film was prepared by copolymerization of tartrazine and acrylamide on the carbon nanotube-modified glassy carbon electrode. The performance of the imprinted sensor was investigated by cyclic voltammetry, differential pulse voltammetry, and electrochemical impedance spectroscopy in detail. Under the optimum conditions, two dynamic linear ranges of 8?×?10^?8 to 1?×?10^?6?mol?L^?1 and 1?×?10^?6 to 1?×?10^?5?mol?L^?1 were obtained, with a detection limit of 2.74?×?10^?8?mol?L^?1(S/N?=?3). This sensor was used successfully for tartrazine determination in beverages.     

The electrode modified with Langmuir–Blodgett film of p-tert-butylcalix[4]arene derivatives with sulfur-containing functionalities for the determination of silver

A new voltammetric sensor, based on a new p-tert-butylcalix[4]arene derivative (TCAD) modified glassy carbon electrode (GCE) using Langmuir–Blodgett (LB) technique, was designed successfully and used for recognition and determination of Ag⁺. The π?-?A isotherms suggested that the monolayer of TCAD can coordinate with Ag⁺ at the air–water surface. Under the optimum experimental conditions, this voltammetric sensor shows a linear voltammetric response for Ag⁺ in the range of 1.0?×?10^?8?～?6.0?×?10^?6?mol?L^?1 with detection limit 5.0?×?10^?9?mol?L^?1. The high sensitivity, selectivity, and stability of this LB film modified electrode also demonstrate its practical application for a simple, rapid and economical determination of Ag⁺ in water sample.     

An Electrochemical Sensor for L-Tryptophan Using a Molecularly Imprinted Polymer Film Produced by Copolymerization of o-Phenylenediamine and Hydroquinone

An electrochemical sensor for L-tryptophan based on a molecularly imprinted polymer was developed. The sensing film was prepared by the co-electropolymerization of o-phenylenediamine and hydroquinone on a gold electrode in the presence of L-tryptophan as the template. The performance of the L-tryptophan sensor was characterized by cyclic voltammetry, differential pulse voltammetry, and alternating current impedance. Under the optimal experimental conditions, the relative current change was linear to the concentration of L-tryptophan in the range of 1.0 × 10^?8 to 1.0 × 10^?6 mol/L and a detection limit of 0.50 × 10^?8 mol/L was obtained. The sensor showed high sensitivity and selectivity for L-tryptophan. The imprinting factor was 3.58 and selectivity factors of L-tryptophan compared to analogs were larger than 2. The sensor also demonstrated good resistance to acidic, basic, and organic environments.     

Voltammetric Determination of Hydroquinone using β‐Cyclodextrin/Poly(N‐Acetylaniline)/Carbon Nanotube Composite Modified Glassy Carbon Electrode

Abstract

An electrochemical sensor for hydroquinone (HQ) using β‐cyclodextrin/poly(N‐acetylaniline)/carbon nanotube composite (β‐CD/PAA/MWNTs) modified glassy carbon electrode has been successfully developed. Based on the synergistic effect of MWNTs and conducting PAA polymer and the accumulation effect of β‐CD, the analytical response of the β‐CD/PAA/MWNTs film to the electrochemical behavior of HQ was better than that of a β‐CD/PAA film, a PAA/MWNTs film, a PAA film, or a bare glassy carbon (GC) electrode. Under the conditions chosen, the anodic currents increased linearly with HQ concentration from 1×10^?6 to 5×10^?3 mol l^?1 and the detection limit was 8×10^?7 mol l^?1. This electrochemical sensor showed excellent reproducibility, stability and recovery for the determination of HQ.     

Preparation of Cobalt Oxide Nanoclusters/Overoxidized Polypyrrole Composite Film Modified Electrode and Its Application in Nonenzymatic Glucose Sensing

A cobalt oxide nanocluster/overoxidized polypyrrole composite film electrochemical sensing interface was fabricated by two step electrochemical method. The electrochemical properties and electrocatalytic activity of the resulting modified electrode were also studied carefully. The results showed that this modified electrode exhibited good stability, good anti‐interference ability, as well as high electrocatalytic activity to the oxidation of glucose. The linear range for the amperometric determination of glucose was 2.0×10^?7–2.4×10^?4 mol L^?1 and 2.4×10^?4–1.4×10^?3 mol L^?1 with a detection limit of 5.0×10^?8 mol L^?1 (S/N=3), respectively. The sensitivity was 1024 µA mM^?1 cm^?2.     

A Selective Cholesterol Biosensor Based on Composite Film Modified Electrode for Amperometric Detection

An amperometric cholesterol biosensor based on immobilization of cholesterol oxidase in a Prussian blue (PB)/polypyrrole (PPy) composite film on the surface of a glassy carbon electrode was fabricated. Hydrogen peroxide produced by the enzymatic reaction was catalytically reduced on the PB film electrode at 0 V with a sensitivity of 39 μA (mol/L)^?1. Cholesterol in the concentration range of 10^?5 ? 10^?4 mol/L was determined with a detection limit of 6 × 10^?7 mol/L by amperometric method. Normal coexisting compounds in the bio‐samples such as ascorbic acid and uric acid do not interfere with the determination. The excellent properties of the sensor in sensitivity and selectivity are attributed to the PB/PPy layer modified on the sensor.     

Electrochemical Sensor Prepared from Molecularly Imprinted Polymer for Recognition of 1,3-Dinitrobenzene (DNB)

An electrochemical sensor was modified with multi‐wall carbon nanotubes (MWCNT) and molecularly imprinted polymer (MIP) material synthesized with acrylamide and ethylene glycol dimethacrylate (EGDMA) in the presence of 1,3‐dinitrobenzene (DNB) as the template molecule. The MWCNT and MIP layers were successively modified on the surface of a glassy carbon electrode (GCE), of which the MIP film works as an artificial receptor due to its specific molecular recognition sites. The MIP material was characterized by FT‐IR and electrochemical methods of square wave voltammetry (SWV). The interferences of other nitroaromatic compounds (NAC) such as 2,4,6‐trinitrotoluene (TNT), 1,3,5‐trinitrobenzene (TNB) and 2,4‐dinitrotoluene (DNT) to DNB were also investigated by the prepared MIP/MWCNT electrode. Compared with other traditional sensors, the MIP/MWCNT modified electrode shows good selectivity and sensitivity. In addition, the current responses to DNB are linear with the concentration ranging from 4.5×10^?8 to 8.5×10^?6 mol/L with the detection limits of 2.5×10^?8 (?0.58 V) and 1.5×10^?8 mol/L (?0.69 V) (S/N=3). The construction process of MIP/MWCNT modified electrode was also studied as well. All results indicate that the MIP/MWCNT modified electrode established an improving way for simple, fast and selective analysis of DNB.     

A Cholesterol Biosensor Based on Entrapment of Cholesterol Oxidase in a Silicic Sol‐Gel Matrix at a Prussian Blue Modified Electrode

A cholesterol biosensors fabricated by immobilization of cholesterol oxidase (ChOx) in a layer of silicic sol‐gel matrix on the top of a Prussian Blue‐modified glassy carbon electrode was prepared. It is based on the detection of hydrogen peroxide produced by ChOx at ?0.05 V. The half‐lifetime of the biosensor is about 35 days. Cholesterol can be determined in the concentration range of 1×10^?6?8×10^?5 mol/L with a detection limit of 1.2×10^?7 mol/L. Normal interfering compounds, such as ascorbic acid and uric acid do not affect the determination. The high sensitivity and outstanding selectivity are attributed to the Prussian Blue film modified on the sensor.     

Sensitive and Selective Detection of Dopamine Using a DNA Immobilized Ethylenedidamine/Polyglutamic Modified Electrode

DNA was attached on the surface of an ethylenedidamine/polyglutamic(En/PGA) modified glassy carbon electrode (GCE) to create a novel voltammetric sensor (DNA/En/PGA/GCE) for dopamine (DA). This modified electrode exhibited a linear voltammetric response for DA in the range from 1.0×10^?7 mol L^?1 to 1×10^?5 mol L^?1, with a detection limit of 2×10^?8 mol L^?1. The detection of DA was found to be unaffected by the presence of ascorbic acid, uric acid, serotonin and folic acid. The method proposed was applied to detect DA in pharmaceutical dosage and human blood serum with good satisfactory results.     

Differential Pulse Voltammetric Determination of Selenocystine and Selenomethionine Using SAM nanoSe0/Vc/SeCys‐Film Modified Au Electrode

The SAM nanoSe⁰/Vc/SeCys‐film modified Au electrode has been prepared to determine selenocystine and selenomethionine. The AFM and SEM showed the special three‐dimensional (3D) network structure of the sol‐gel films. The affinity between nanoparticles and biomolecules created special chemical characters analyzed by the XRD and fluorescence. The modified electrode was characterized by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The modified films partly had resistance in the charge transduction of Fe(CN) , but the less electron‐transfer resistance. Differential pulse voltammetric (DPV) determination of selenoamino acids using SAM nanoSe⁰/Vc/SeCys‐film modified Au electrode was presented. In PBS (pH 7.0)+0.1 mol L^?1 NaClO₄ solution, selenoamino acids yielded a sensitive reduction peak at about +400±50 mV. The peak current had a linear relationship with the concentration of selenoamino acids in the range of 5.0×10^?8–1.0×10^?5 mol L^?1, and a 3σ detection limit of selenoamino acids was 1.2×10^?8 mol L^?1. The relative standard deviation of DPV signals of 0.50×10^?6 mol L^?1 selenoamino acids was 3.8% (n=8) using the same electrode and was 4.4% (n=5) when using three modified electrodes prepared at different times. The content of selenoamino acids in the organo‐selenium powder were determined by DPV. The results showed 71.5 μg g^?1 of SeCys and 65.1 μg g^?1 of SeMet in the organo‐selenium powder.     

Sol—Gel Derived Carbon Ceramic Electrode Bulk—Modified with Tris（1,10—phenanthroline—5,6—dione） iron （Ⅱ）Hexafluorophosphate and Its Use as an Amperometric Iodate Sensor

A surface‐renewable tris(1, 10‐phenanthroline‐5, 6‐dione) iron (D) hexafluorophosphate (FePD) modified carbon ceramic electrode was constructed by dispersing FePD and graphite powder in methyltrimethoxysilane (MTMOS) based gels. The FePD‐modified electrode presented pH‐dependent voltammetric behavior, and its peak currents were diffusion‐controlled in 0.1 mol/L Na₂SO₄ + H₂SO₄ solution (pH = 0.4). In the presence of iodate, dear electrocatalytic reduction waves were observed and thus the chemically modified electrode was used as an amperometric sensor for iodate in common salt. The linear range, sensitivity, detection limit and response time of the iodate sensor were 5 × 10^?6–1 × 10^?2 mol/L, 7.448 μA·L/ mmol, 1.2 × 10^?6 mol/L and 5 s, respectively. A distinct advantage of this sensor is its good reproducibility of surface‐renewal by simple mechanical polishing.     

Stability Improvement of Prussian Blue by a Protective Cellulose Acetate Membrane for Hydrogen Peroxide Sensing in Neutral Media

The cellulose acetate covered Prussian blue modified glassy carbon electrode (GCE/PB/CA) was fabricated as a novel hydrogen peroxide sensor. It was shown by scanning electron microscope (SEM) and atomic force microscope (AFM) that Prussian blue was covered and protected by cellulose acetate perfectly. The modified electrode showed a good electrocatalytic activity for H₂O₂ reduction in neutral aqueous solution. H₂O₂ was detected amperometrically in 0.05 mol/L phosphate buffer solutions (pH 7.0, containing 0.1 mol/L KCl as supporting electrolyte) at an applied potential of ?0.2 V (vs. SCE). The response current was proportional to the concentration of H₂O₂ in the range of 1.0×10^?5 mol/L to 2.5×10^?4 mol/L with the detection limit of 2.2×10^?6 mol/L at a signal to noise ratio 3.     

Direct electrochemistry of glucose oxidase immobilized on TiO2–graphene/nickel oxide nanocomposite film and its application

A novel electrochemical platform based on nickel oxide (NiO) nanoparticles and TiO₂–graphene (TiO₂–Gr) was developed for the direct electrochemistry of glucose oxidase (GOD). The electrochemical behavior of the sensor was studied using cyclic voltammetry and chronoamperometry. The experimental results demonstrated that the nanocomposite well retained the activity of GOD and the modified electrode GOD/NiO/TiO₂–Gr/GCE exhibited excellent electrocatalytic activity toward the redox of GOD as evidenced by the significant enhancement of redox peak currents in comparison with bare GCE. The biosensor responded linearly to glucose in the range of 1.0–12.0?mM, with a sensitivity of 4.129?μA?mM^?1 and a detection limit of 1.2?×?10^?6?M under optimized conditions. The response time of the biosensor was 3?s. In addition, the developed biosensor possessed good reproducibility and stability, and there was negligible interference from other electroactive components.     

Electrochemical Biosensing Platforms Using Phthalocyanine‐Functionalized Carbon Nanotube Electrode

Iron‐phthalocyanines (FePc) are functionalized at multi‐walled carbon nanotubes (MWNTs) to remarkably improve the sensitivity toward hydrogen peroxide. We constructed a highly sensitive and selective glucose sensor on FePc‐MWNTs electrode based on the immobilization of glucose oxidase (GOD) on poly‐o‐aminophenol (POAP)‐electropolymerized electrode surface. SEM images indicate that GOD enzymes trapped in POAP film tend to deposit primarily on the curved tips and evenly disperse along the sidewalls. The resulting GOD^@POAP/FePc‐MWNTs biosensor exhibits excellent performance for glucose with a rapid response (less than 8 s), a wide linear range (up to 4.0×10^?3 M), low detection limits (2.0×10^?7 M with a signal‐to‐noise of 3), a highly reproducible response (RSD of 2.6%), and long‐term stability (120 days). Such characteristics may be attributed to the catalytic activity of FePc and carbon nanotube, permselectivity of POAP film, as well as the large surface area of carbon nanotube materials.